WASHINGTON (CNN) --A soldier wounded in a grenade attack at a 101st Airborne Division base in Kuwait has died, U.S. Central Command said.

Another soldier attached to the 101st is being questioned in connection with the fatal grenade and small arms attack at one of the division's camps in northern Kuwait, Army V Corps spokesman Max Blumenfeld said early Sunday in Kuwait. U.S. military officials said 12 soldiers were wounded, at least five of them seriously.

A brigade commander said the soldier in custody lobbed three grenades into the three tents housing commanding officers from the tactical operations center, according to a reporter embedded with the unit. (Full story)

Meanwhile, a Royal Air Force aircraft returning from a mission in Iraq has gone missing, British military officials in the region said Sunday.

While ground forces pushed ahead elsewhere, U.S. and British tanks and troops clashed with Iraqi forces in the southern port city of Umm Qasr.

On Saturday, coalition forces struck Iraqi targets with bombs and missiles, while lead elements of the U.S. Army's 3rd Infantry Division crossed the Euphrates River and pushed to within 160 miles [260 kilometers] of Baghdad -- about halfway to the Iraqi capital from Kuwait, the Pentagon said.

Elsewhere in northern Kuwait, an Iraqi missile was fired at a U.S. post and was destroyed in the air by two Patriot missiles. The missile contained no chemical agents, U.S. commanders said.

Gen. Tommy Franks, head of U.S. Central Command, speaking Saturday at his Persian Gulf base of operations in Qatar, promised that the Iraqi campaign would be "unlike any other in history."

He said that though he is "satisfied" with the progress so far, he warned "there may well be tough days ahead." Promising overall victory, he said the war's "outcome is not in doubt." (Full story)

The northern cities of Mosul and Kirkuk, major oil-producing centers, were the target of bombing for the third night in a row Saturday night.

Kurdish intelligence, which has sources in Mosul, told CNN the targets included a palace belonging to Saddam Hussein, a major military barracks and the local headquarters of Iraqi military intelligence. (Full story)

The Kirkuk airfield also was bombed. A large air base with many underground bunkers and ammunition storage facilities, the airport could be important to coalition forces to secure the northern parts of Iraq.

So far, there is no significant presence of U.S. ground troops in the north.

Meanwhile, more explosions rattled the Iraqi capital Saturday night and early Sunday morning, and towers of smoke filled the skies above the city.

At the outskirts of Basra, Iraq's second-largest city, coalition forces skirmished with Iraqi troops. They surrounded the city and opted not to try to occupy it.

Casualties among troops, reporters

An American and six Britons were killed Saturday when two British Navy helicopters crashed. That brought the total number of coalition deaths to 21 -- 14 Britons and seven Americans. Two have died in combat, the rest in helicopter crashes.

Also three British journalists were reported missing Saturday near Basra.

In a Kurdish region of northern Iraq, a freelance cameraman working for the Australian Broadcasting Corp., Paul Moran, 39, died when a taxicab exploded at a checkpoint in Sayed Sadiq, the network said. Three Kurdish fighters also died, and an ABC correspondent was wounded, it said.

Security officials of the Patriotic Union of Kurdistan blamed the blast on a suicide bomber from an Islamic extremist group, Ansar al-Islam, which U.S. officials believe has links to al Qaeda.

Franks said an Ansar al-Islam camp in northern Iraq near the Iranian border was struck by a cruise missile during Saturday's air campaign.

A top Pentagon official acknowledged Saturday that delays in moving U.S. forces into northern Iraq, caused by prolonged negotiations with Turkey about moving them across its territory, means that the security of the oil fields around Kirkuk cannot be assured until a northern front can be established.

Now that efforts to secure basing rights in Turkey have been abandoned, more than 30 cargo ships carrying heavy combat equipment for the 4th Infantry Division that waited for weeks off Turkey's coast are beginning to move through the Suez Canal, heading for Kuwait.

"We will still have a northern option at some point," a Pentagon official said, but declined to provide details on when might happen.

Other developments

• A Tomahawk cruise missile might have missed its target in Iraq and landed in southwest Iran, Pentagon officials said Saturday. Military officials were investigating. Hundreds of cruise missiles were fired during coalition attacks Friday.

• There were conflicting reports whether Turkish troops have crossed the border into Iraq. The Turks contend they need a buffer zone in northern Iraq to "manage the humanitarian situation" -- partly by keeping Kurdish refugees from crossing into Turkey. U.S. officials do not want Turkish troops moving into Kurdish-controlled areas of northern Iraq for fear of clashes between Turkish and Kurdish troops.